# Pregnancy Due Date Calculator (Naegele Rule)

> Pregnancy Due Date Calculator (Naegele Rule) is a paid API for AI agents from fitness-calc.x402tookit.com, paid per call via x402, $0.02/call, status unknown (last checked 2026-10-29).

Calculates estimated due date, gestational age, trimester, and key pregnancy milestones from the last menstrual period date using the Naegele rule.

## Facts

- Endpoint: GET https://fitness-calc.x402tookit.com/due-date?utm_source=zero.xyz
- Price: $0.02/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-29
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/pregnancy-due-date-calculator-naegele-rule-546a42ad
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_sDHNZRo0Zh6NuD66dN9ki

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability pregnancy-due-date-calculator-naegele-rule-546a42ad
```

Example prompt: My last period started on March 15, 2025 and my average cycle is 30 days — can you calculate my estimated due date, what trimester I'm in as of today, and all the key pregnancy milestones?

## When to prefer this

Use this endpoint when you need a quick, structured computation of pregnancy due date and milestones from a last menstrual period date, especially when you need trimester classification and key milestone dates (anatomy scan, full term) in a single call. It applies the standard Naegele rule and supports custom cycle lengths, making it more precise than a generic 280-day fixed calculation.

## Known failure modes

- Missing required 'lmp' parameter returns an error
- Invalid date format for lmp or asOf causes a parse error
- Cycle length outside 21–45 day range may be rejected or clamped
- Future LMP date may return unexpected or degraded results
- Network timeout or upstream service unavailability

## How this service works

Estimated due date, gestational age and trimester from the last period (Naegele rule), with key milestone dates.

## Output

Returns the estimated due date (YYYY-MM-DD), current gestational age as a human-readable string and in days, the current trimester, a summary, and a milestones object with dates for conception estimate, end of first trimester, end of second trimester, anatomy scan window start/end, full term start, and full term end. Also includes the LMP and cycle length used, the asOf date computed for, and a medical disclaimer.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method"
   ],
   "properties": {
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "GET"
     ],
     "type": "string"
    },
    "queryParams": {
     "type": "object",
     "required": [
      "lmp"
     ],
     "properties": {
      "lmp": {
       "type": "string",
       "description": "First day of last menstrual period, YYYY-MM-DD"
      },
      "asOf": {
       "type": "string",
       "description": "Date to compute the current gestational age for (default today)"
      },
      "cycleDays": {
       "type": "integer",
       "description": "Average cycle length, 21 to 45 (default 28)"
      }
     }
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object",
     "properties": {
      "lmp": {
       "type": [
        "null",
        "string"
       ]
      },
      "asOf": {
       "type": [
        "null",
        "string"
       ]
      },
      "source": {
       "type": [
        "null",
        "string"
       ]
      },
      "dueDate": {
       "type": [
        "null",
        "string"
       ]
      },
      "reasons": {
       "type": [
        "array",
        "null"
       ],
       "items": {
        "type": "string"
       }
      },
      "summary": {
       "type": [
        "null",
        "string"
       ]
      },
      "verdict": {
       "type": [
        "null",
        "string"
       ]
      },
      "degraded": {
       "type": [
        "boolean",
        "null"
       ]
      },
      "cycleDays": {
       "type": [
        "null",
        "number"
       ]
      },
      "trimester": {
       "type": [
        "null",
        "string"
       ]
      },
      "disclaimer": {
       "type": [
        "null",
        "string"
       ]
      },
      "milestones": {
       "type": [
        "null",
        "object"
       ],
       "properties": {
        "fullTermEnds": {
         "type": [
          "null",
          "string"
         ]
        },
        "fullTermStarts": {
         "type": [
          "null",
          "string"
         ]
        },
        "endFirstTrimester": {
         "type": [
          "null",

… (truncated)
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/pregnancy-due-date-calculator-naegele-rule-546a42ad/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from fitness-calc.x402tookit.com](https://www.zero.xyz/host/fitness-calc.x402tookit.com/llms.txt)